import {cleanUpLine} from "../line/line_data.js"
import {indexOf} from "../util/misc.js"
import {signalLater} from "../util/operation_group.js"

// The document is represented as a BTree consisting of leaves, with
// chunk of lines in them, and branches, with up to ten leaves or
// other branch nodes below them. The top node is always a branch
// node, and is the document object itself (meaning it has
// additional methods and properties).
//
// All nodes have parent links. The tree is used both to go from
// line numbers to line objects, and to go from objects to numbers.
// It also indexes by height, and is used to convert between height
// and line object, and to find the total height of the document.
//
// See also http://marijnhaverbeke.nl/blog/codemirror-line-tree.html

export function LeafChunk(lines) {
    this.lines = lines
    this.parent = null
    let height = 0
    for (let i = 0; i < lines.length; ++i) {
        lines[i].parent = this
        height += lines[i].height
    }
    this.height = height
}

LeafChunk.prototype = {
    chunkSize() {
        return this.lines.length
    },

    // Remove the n lines at offset 'at'.
    removeInner(at, n) {
        for (let i = at, e = at + n; i < e; ++i) {
            let line = this.lines[i]
            this.height -= line.height
            cleanUpLine(line)
            signalLater(line, "delete")
        }
        this.lines.splice(at, n)
    },

    // Helper used to collapse a small branch into a single leaf.
    collapse(lines) {
        lines.push.apply(lines, this.lines)
    },

    // Insert the given array of lines at offset 'at', count them as
    // having the given height.
    insertInner(at, lines, height) {
        this.height += height
        this.lines = this.lines.slice(0, at).concat(lines).concat(this.lines.slice(at))
        for (let i = 0; i < lines.length; ++i) lines[i].parent = this
    },

    // Used to iterate over a part of the tree.
    iterN(at, n, op) {
        for (let e = at + n; at < e; ++at)
            if (op(this.lines[at])) return true
    }
}

export function BranchChunk(children) {
    this.children = children
    let size = 0, height = 0
    for (let i = 0; i < children.length; ++i) {
        let ch = children[i]
        size += ch.chunkSize();
        height += ch.height
        ch.parent = this
    }
    this.size = size
    this.height = height
    this.parent = null
}

BranchChunk.prototype = {
    chunkSize() {
        return this.size
    },

    removeInner(at, n) {
        this.size -= n
        for (let i = 0; i < this.children.length; ++i) {
            let child = this.children[i], sz = child.chunkSize()
            if (at < sz) {
                let rm = Math.min(n, sz - at), oldHeight = child.height
                child.removeInner(at, rm)
                this.height -= oldHeight - child.height
                if (sz == rm) {
                    this.children.splice(i--, 1);
                    child.parent = null
                }
                if ((n -= rm) == 0) break
                at = 0
            } else at -= sz
        }
        // If the result is smaller than 25 lines, ensure that it is a
        // single leaf node.
        if (this.size - n < 25 &&
            (this.children.length > 1 || !(this.children[0] instanceof LeafChunk))) {
            let lines = []
            this.collapse(lines)
            this.children = [new LeafChunk(lines)]
            this.children[0].parent = this
        }
    },

    collapse(lines) {
        for (let i = 0; i < this.children.length; ++i) this.children[i].collapse(lines)
    },

    insertInner(at, lines, height) {
        this.size += lines.length
        this.height += height
        for (let i = 0; i < this.children.length; ++i) {
            let child = this.children[i], sz = child.chunkSize()
            if (at <= sz) {
                child.insertInner(at, lines, height)
                if (child.lines && child.lines.length > 50) {
                    // To avoid memory thrashing when child.lines is huge (e.g. first view of a large file), it's never spliced.
                    // Instead, small slices are taken. They're taken in order because sequential memory accesses are fastest.
                    let remaining = child.lines.length % 25 + 25
                    for (let pos = remaining; pos < child.lines.length;) {
                        let leaf = new LeafChunk(child.lines.slice(pos, pos += 25))
                        child.height -= leaf.height
                        this.children.splice(++i, 0, leaf)
                        leaf.parent = this
                    }
                    child.lines = child.lines.slice(0, remaining)
                    this.maybeSpill()
                }
                break
            }
            at -= sz
        }
    },

    // When a node has grown, check whether it should be split.
    maybeSpill() {
        if (this.children.length <= 10) return
        let me = this
        do {
            let spilled = me.children.splice(me.children.length - 5, 5)
            let sibling = new BranchChunk(spilled)
            if (!me.parent) { // Become the parent node
                let copy = new BranchChunk(me.children)
                copy.parent = me
                me.children = [copy, sibling]
                me = copy
            } else {
                me.size -= sibling.size
                me.height -= sibling.height
                let myIndex = indexOf(me.parent.children, me)
                me.parent.children.splice(myIndex + 1, 0, sibling)
            }
            sibling.parent = me.parent
        } while (me.children.length > 10)
        me.parent.maybeSpill()
    },

    iterN(at, n, op) {
        for (let i = 0; i < this.children.length; ++i) {
            let child = this.children[i], sz = child.chunkSize()
            if (at < sz) {
                let used = Math.min(n, sz - at)
                if (child.iterN(at, used, op)) return true
                if ((n -= used) == 0) break
                at = 0
            } else at -= sz
        }
    }
}
